High-frequency heating



y 15, 1952 A. G. SEIFRIED ETAL 2,603,741

HIGH-FREQUENCY HEATING mikes infirm E'SEZEi'Ed Filed Dec. 12, 1946 fil 'am L-J'snkins 74A WI 279 un sww SR. QvJ

Patented July 15, 1952 HIGH-FREQUENCY HEATING Anton G. Seifried and William L. Jenkins, Akron,

Ohio, assignors to The B. F. Goodrich Company, New York, N. Y., a corporation of New York Application December 12, 1946, Serial No. 715,882

4 Claims.

trically heated by subjecting the material to electrical energy waves in the frequency range of 8 to 200 megacycles which induced oscillation in the molecules of the material and caused frictional heating.

The previously employed dielectric heating methods were not readily applicable to oddshaped articles or articles of non-uniform cross H section because paired electrodes had to be used. It was often difficult to position the electrodes in odd-shaped articles, and varied current intensities could not be obtained unless a plurality of paired electrodes were used or the current intensity was varied by loss in an air gap. Such methods involved cumbersome equipment and inefiicient use of the expended energy. Furthermore, voltages of 5,000 volts or greater were commonly used to insure complete penetration of the material being heated, and this caused arcing or break-down of the dielectric material between the paired electrodes and between particles of th material being heated.

This invention concerns the use of micro waves having a frequency of at least 500 megacycles per second for heating of thermoplastic dielectric material such as thermosetting materials or vulcanizable compositions. By means of this invention such materials, even though comprising relatively large molecules, are quickly and uniformly at voltages sufficiently low to minimize or sub stantially eliminate arcing. Articles of odd shapes can be readily vulcanized, since paired electrodes are not necessary with directionally emitted waves such as are used in this invention. Noelaborate control equipment is necessary and the complex circuits formerly used are eliminated. It is an object of this invention to utilize the light-like characteristics of micro waves which constitute the range between waves of 50 cm. in length and about 1 cm. in length. By means of this invention, directed beams of high pentrating power are used to heat materials such as rubber at voltages below 1,000 volts. A further object of this invention is to uniformly heat thermoplastic .heated with efficient use of the expended energy dielectric articles of non-uniform cross section by taking advantage of the reflectable nature of the waves to attain a beam of varying cross-sectional intensity in conformance with the configuration of the articles being heated. Other objects of this invention are to provide apparatus for the continuous heating of large articles or a plurality of articles and to provide reflecting means so that the emergent portion of the waves which have penetrated through the article being heated are reflected back into the article.

The invention may be illustrated by reference to a preferred apparatus as illustrated in the accompanying drawings of which:

Fig. 1 is a view in elevation of apparatus for continuous vulcanization of rubber by means of micro waves, part being broken away for clarity of illustration;

Fig. 2 is a section taken on line 2-2 of Fig. 1;

Fig. 3 is a fragmentary plan view of a multiple cavity mold which may be used in conjunction with apparatus shown in Fig. 1 for vulcanizing a plurality of articles; and

Fig. 4 is a section on line 4+4 of Fig. 3.

In the preferred embodiment as illustrated by the drawings the heating apparatus comprises a generally rectangular skeletal supporting frame I 0 having four angle iron uprights II, II rigidly secured together in a box-like structure by means of four horizontal lower connecting beams I2, I2 and a pair of angle iron upper cross "beams I3, I3 secured to the top of the uprights and extending lengthwise of the rectangular frame.

Each L-shaped upper bean I3 has a plurality of holes I4, Hi drilled through the verticalportion of the beam with horizontal brackets I5, l5 secured to the bed of the beam opposite each hole. Each bracket I5 houses one end of a pin I6 rigidly held therein by means of a set screw I I with the free end of the pin extending through the hole opposite the bracket and terminating in an enlarged head I 8. A dolly wheel I9 is journalled on each pin I6 between the upper beam I2 and the enlarged head I8.

Spaced along the vertical portion of each upper cross beam I 3, between the holes I I, I4, are vertical brackets 25, 20' which are rigidly fastened to the beam. Each vertical bracket 20 holds a vertical pin 2i similar to the horizontal pins l6, IS with one end of the vertical pin being held in the bracket and the free end of the pin extending above the beam I3 and terminating in an enlarged head 22. A roller guide wheel 23 is journailed on each vertical pin 21 between the enlarged pin head 22 and the bracket 20 with its periphery extending beyond the inner faceof the cross beam. 9

At each end of the apparatus a pair of large support wheels 24 and 25 and a sprocket drive wheel 26 (Fig. 2) are keyed to the rotatable shafts 21 and 21a. Each of the shafts is journalled in a pair of bracket bearings 28, 28 fastened to the uprights. The support wheels 24 and 25 are mounted on the respective shafts just inside the uprights and the respective sprocket wheels 26, 26 are mounted at the centers of the shafts.

An electric motor 29 and gear box 39 are fastened to a plate 3! which is secured to the lower cross beams I 2, l 2 near one end of the apparatus. The motor rotates drive shaft 21a by means of a positive chain drive 32.

An endless flexible metal conveyor 33 is positioned around the large support wheels 24 and 25 on each end of the frame l0, the upper reach of the conveyor being supported by the series of dolly wheels l9, [9 between the guide Wheels 23, 23. Conveyor 33 comprises a plurality of supporting elements 34, 34 generally U-shaped in transverse section, joined together by hinges 35, 35.

The sprocket wheels 26, 26 are provided with cogs 36, 36 adapted to engage driving teeth 31, 3! on the back of the respective supporting elements 34, 34. I'he cogs 36, 36 are bifurcated as at 38, 38 to accommodate hinges 35, 35 between supporting elements 34, 34.

In this preferred embodiment for continuously vulcanizing strip rubber stock the stock 39 is fed onto the upper reach of conveyor 33 by means of an auxiliary conveyor belt feed 40 which is supported on a pulley wheel 4! keyed to a rotatable shaft 42 journalled in a bracket bearing 43 which is secured to an auxiliary supporting frame 44. This feed conveyor is actuated from driven shaft 2'! by means of a chain and sprocket drive 45. By selecting sprockets of appropriate sizes the linear speed of the feed conveyor 49 and the conveyor 33 may be synchronized.

The strip stock 39 is taken off the heating apparatus on a take-off conveyor belt 40a riding on pulley 41a, which is keyed to rotatable shaft 42a journalled in bracket bearing 43a secured to auxiliary support frame 44a. The take-off conveyor is actuated by chain and sprocket drive 45a from drive shaft 21a.

The heating means for the apparatus comprises two magnetron tubes 46, 46 which act as self-contained oscillator circuits to directionally emit micro waves which have essentially linear path characteristics. The magnetron tubes 46, 46 are joined to a source of direct current (not shown) by means of lead-in wires 41, 41. The magnetron tubes are let into the enclosed upper ends 48, 48 of a pair of Wave guide members 49, 49 which are hung from an overhead carrying frame 59. Frame 59 in turn is suspended from an I-beam by means of bolts 52, 52. The I-beam is rigidly held in place by means of external supporting beams (not shown).

The wave guide members 49, 49 comprise inverted generally box-like members having a closed upper end 48 and flaring sides 53, 53, with an open bottom. The wave guides extend downwardly so that the lower edges 54. 54 of the guide are positioned just above the vertical edges 55, 55 of the conveyor 33 as the conveyor passes over the top of the supporting frame Hi. The inner surfaces 56, 56 of wave guides 49, 49 preferably comprise polished metal such as polished steel,

chromium, etc., adapted to reflect the emitted micro waves as indicated by the broken lines in Fig. 1. The inner surface 51 of the metal conveyor 33 also comprises polished metal adapted to reflect the emergent portion of the micro Waves which have passed completely through the rubber stock on the conveyor. The reflected portions thus serve to further heat the rubber, and the energy is not wasted.

In operating the preferred apparatus the rubber stock is continuously conveyed through the directed path of emitted micro waves which have a frequency in the range of 500 to about 30,000 megacycles and preferably above 1,000 megacycles. The rate of movement of the stock through the path of the waves is chosen in view of the particular compound that is being heated and the thickness of the article so that the stock is vulcanized to the desired degree upon emergence.

It is preferable that the rubber stock be directly exposed to the directed beam of micro waves as the rubber stock is conveyed through the wave beam, as shown in Fig. 2.

A modified form of the apparatus is also applicable for heating a plurality of articles such as molded rubber washers. In such a case the only changes necessary are in the design of the conveyor 33. In this modification a conveyor 58 having a plurality of mold cavities 59, 59 in each suporting member 60 is used as illustrated in Fig. 3. The supporting member 60, 60 of the conveyor are provided with hinges 6|, 6| as before, and each member has a driving tooth 62 on its back face 63. The individual articles 64, 64 are heated as before by passing the stock through the path of the directed micro waves. as can readily be seen in Fig. l, and preferably directly exposed thereto, as shown in Fig. 4. The emitted micro waves are directed against a wave guide of suitable configuration and reflected back in a beam varying in intensity across its face for heating articles of non-uniform cross section. This is made possible because of the lightlike wave characteristics of micro Waves such as are used in practicing this invention. The configuration of the guide member is selected so that the directed beam attained thereby has a varying cross sectional intensity such that the thicker portion of the material being heated may be disposed in themore intense portion of the beam.

The invention is applicable to heating any thermoplastic dielectric material and is particularly applicable to thermosetting materials, whether thermosetting resins as exemplified by the phenol formaldehyde resins and similar resins, or vulcanizable compositions such as compositions comprising either natural or synthetic rubber. The stock to be vulcanized may be either strip stock, molded articles, sponge stock or any of the manifold variations which are commonly used in rubber compounding. The sponge stock may comprise thermoplastic material as plasticized polyvinyl chloride, etc., as well as the ordinary rubber sponge stock.

By means of this invention such materials as rubber are dielectrically heated quickly and uniformly with micro waves which exhibit many of the characteristics of light waves. Since micro Waves, that is waves having frequencies in the range of 500 to about 30,000 megacycles, are directionally emitted from a single source and travel in a substantially straight line upon emission, it is not necessary to use pairs of electrodes to determine the current path. Ultra high frequency waves such as are used in this invention in addition to linear path characteristics are reficctable, and thus the' emergent portion of desired. This allows the heating of rubber stock' without the necessity of obtaining as complete dispersion of the loading materials as was formerly necessary. This was not possible when heating with waves having frequencies below 200 megacycles, since voltages of the order of 5,000 volts were commonly used to insure complete penetration of the material being heated.

High frequency waves of the order of 500 megacycles per second or greater are obtained by the use of a relatively simple installation. Magnetron tubes act as a complete oscillator circuit and directionally emit micro waves. In a typical industrial installation it is necessary only to furnish a source of direct current to the magnetron tube. A preferred form of tube is the cavity magnetron preferably provided with a water-cooled jacket, although any suitable source of directionally emitted micro waves may be used. This obviates the necessity of elaborate control equipment which must be used with paired electrodes. Since the waves are directionally emitted without the use of paired electrodes the difliculties involved in placing suitable paired electrodes in odd shaped articles are also obviated. The apparatus used in practicing this invention is relatively simple and no elaborate control equipment is necessary.

The preferred embodiment of the invention has been described in considerable detail, but variations and modifications of the apparatus may be effected within the scope of this invention and changes may be made in the method within the scope of this invention as defined in the appended claims.

We claim:

1. The method of uniformly heating a vulcanizable article of non-uniform cross section which comprises generating directionally emitted electrical energy waves having a frequency greater than 500 megacycles and a voltage below 1000 volts, focusing said waves into a directed beam adapted to provide varying wave intensities in different portions of the beam, disposing the article in the path of said beam with the thicker portions of the article in the path of the more intense portions of the beam, and reflect-- ing the emergent portion of the beam back into said article.

2. Apparatus for vulcanizing vulcanizable rubbery material which comprises a high-frequency magnetron adapted to directionally emit micro waves having substantially linear path characteristics and a voltage below 1000 volts, a focusing polished metal open-end wave guide member positioned about said magnetron directing said waves outwardly through the open end of the member in a directed beam, an endless conveyor comprising a plurality of hinged sections presenting a polished metal outer face adapted to reflect micro waves, said conveyor being spaced from said wave guide member and disposed to continuously present a polished metal surface to the open end of the guide member generally normal to the path of said directed beam, a feed means adapted to continuously feed rubbery material on to said conveyor surface in advance of its passage before the open end of said guide member, and driving means adapted to synchronously actuate said feed means and advance said conveyor with said material thereon past the open end of said guide member.

3. The method of uniformly vulcanizing a vulcanizable article of non-uniform cross section which comprises generating directionally emitted electrical energy waves having a frequency of at least 500 megacycles per second and a voltage below 1,000 volts, focusing said waves into a directed beam of said waves, said beam adapted to provide varying wave intensities in different portions of the beam, disposing said article in the direct path of said beam with the thicker portions of the article in the path of the more intense portions of the beam, and reflecting the emergent portion of the beam back into said article.

4. Apparatus for vulcanizing vulcanizable rubbery material which comprises a high-frequency magnetron adapted to directionally emit micro waves having substantially linear path characteristics and a voltage below 1,000 volts, a focusing polished metal open-end wave guide member positioned about said magnetron directing said waves outwardly through the open end of said wave guide member in a directed beam, an endless conveyor having a polished metal outer face adapted to reflect micro waves, said conveyor being spaced from said wave guide member and disposed to continuously present said polished metal face to the open end of the wave guide member generally normal to the path of said directed beam, a feed means adapted to continuously feed rubbery material on to said c0n veyor surface in advance of its passage before the open end of said guide member, and driving means adapted to synchronously actuate said feed means and advance said conveyor with said material thereon past the open end of said guide member.

ANTON G. SEIFRIED. WILLIAM L. JENKINS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,900,573 McArthur Mar. 7, 1933 2,259,318 Mouromtseff Oct. 14, 1941 2,296,948 Pitman Sept. 29, 1942 2,318,533 Selvig May 4, 1943 2,395,920 Te Grotenhuis Mar. 5, 1946 2,407,690 Southworth Sept. 17, 1946 2,421,097 Lakso May 27, 1947 2,427,094 Evans Sept, 9, 1947 2,463,288 Leguillon Mar. 1, 1949 2,467,230 Revercomb et al. Apr. 12, 1949 2,480,682 Stiefel Aug. 30, 1949 2,495,170 Kinn Jan. 17, 1950 2,495,415 Marshall Jan. 24, 1950 2,495,429 Spencer Jan. 24, 1950 2,500,752 Hanson et a1 Mar. 14, 1950 OTHER REFERENCES Hutcheson, Electronic Torch, The Welding Engineer, December 1945, page 90. 

